#include <thread>
#include <iostream>
#include <cassert>
#include <chrono>
#include <mutex>

int counter = 65535;
std::mutex mtx = {};

void worker(int delta) {
	for (auto i = 0U; i < 100; ++i) {
		std::this_thread::sleep_for(std::chrono::milliseconds(20));
		// Zła praktyka! Zawsze rób to RAII!
		// mtx.lock();
		{ // Critical section
			std::lock_guard<std::mutex> _(mtx);
			counter += delta;
		}  
		// mtx.unlock();
	}
}

int main() {
	auto t1 = std::thread(worker, 1);
	auto t2 = std::thread(worker, -1);

	t2.join();
	t1.join();
	assert(counter == 65535);
}